QB 5 



^2 



N° 106 



From, 'The Observatory,' Nos. 350 and 351, November 
and December 1904.] 



A I ) D R ESS 

DELIVERED BY 

H. H. TURNER, D.Sc, F.R.S., 

SAV1LIAX PRol'ESSOl! 01' ASlUHMiMY IX THE (JNIVERSITY OF OXFOI 



SECTION OF ASTROPHYSICS 



at Tin-: 



Congress or Arts ana Sciences at St. £ouis, 



WEDNESDAY, SEPTEMBER 21, 1904, at 4 p.m. 



[From ' The Observatory,' Nos. 350 and 351, November 
and December, t 904.] 



ADDRESS delivered by H. H. TUENER, D.Sc, P.E.S., 
Savilian Professor of Astronomy in the University of 
Oxford, in the Section of Astrophysics at the Congress 
of Arts and Sciences at St. Louis, on Wednesday, 
Sept. 21, 1904, at 4 p.m. 



The European astronomers here present have to thank the 
organizers of this Congress for much more than their hospitable 
invitation to attend it, and the opportunities thus afforded of 
meeting here in St. Louis so many men eminent in there own or 
other branches of knowledge : over and above this they owe to 
them opportunities of seeing the great observatories which have 
developed so rapidly in this country during the last quarter of a 
century, and of admiring at close view the resources and the work 
of which the fame had already reached us across the Atlantic. 
This is not the time or the place for any account of what we have 
seen and learnt ; but not to put on record a word or two of appre- 
ciation of the great works accomplished, and of that munificence 
on the part of American citizens which has rendered them possible, 
would be indeed an omission. We from Europe are, in at least 
one respect, critics well qualified to judge whether an adequate 
return is being obtained for endowments such as have recently fallen 
to the happy lot of American astronomers, for most of us have had 
some practice in the use of such endowments — hypothetical! ij. 
The constraints of more modest equipments have inevitably sug- 
gested plans for work on a larger scale — observatories-in-the-air 
which our imaginations fill with beautiful and novel apparatus, 
where the preliminary trials are always successful and no mistakes 
are made. We come to you accordingly prepared to judge what we 
see by comparison with a very high standard, and you may well 
be content with the commendation which we offer unstinted. We 1/ 

73024 



rejoice to think that, in the presence of the new and vast possi- 
bilities opened up by the gradual accumulation of facts during the 
last century, by the invention of the spectroscope, and by that of 
the photographic plate, Astronomy should be so fortunate as to 
receive valuable aid just at a time when it is so urgently needed. 
It may be well for us to glance for a moment on the other side of 
the picture, and to wonder what would have been the course of 
events if this timely aid had uot come. How would Astrophysics, 
the new-born child of Astronomy, have been nourished ? We can 
scarcely think that it would have been allowed to want for nutriment, 
but whatever was given to it must inevitably have been withdrawn 
from the scanty stock of the parent science ; either parent or 
child, it not both, must have shown signs of starvation. This 
danger is by no means entirely averted even yet ; the needs of 
both, especially of the youthful Astrophysics, are increasing daily, 
as in the case of any other young and healthy organism. The 
future is not free from anxiety ; but that the present is not actually 
a time of distress is largely due to the generosity displayed towards 
our science on this side of the Atlantic. 

I am tempted to make a remark regarding another science, sug- 
gested by the above considerations in conjunction with incidents 
of travel. No one can cross this great continent and note the 
extraordinarily rapid spread of civilization, without feeling his 
interest drawn forcibly to the remnants of the former state of 
things ; to the few remaining native tribes and the monuments of 
their ancestors scattered through the land. No man of science, 
whatever his main interest may be, can be insensible to the vital 
importance of securing permanent records of these vestiges before 
they inevitably perish. No astronomer who is properly grateful 
for the endowment of his own science in time of need can fail to 
hope that the science of Anthropology may be equally fortunate at 
a most critical juncture. I have not the means of knowing whether 
the vanishing opportunities are being properly cared for: I earnestly 
hope it may be so ; but, if it is not, surely this great assembly of 
men from all sciences and nations could not unite to better purpose 
than to urge on the American nation the supreme importance of 
special assistance to Anthropology at the present time. We all 
have needs, even pressing needs, but the pressure is not usually of 
this kind. The subject-matter of our investigations is not 
evanescent; we astronmers, for instance, know that if we must 
perforce put aside a particular investigation for lack of means, fifty 
years hence a more fortunate successor will find the eternal heavens 
little changed for the same purpose. But the anthropologist cannot 
wait ; with him it is now or never, and Science would be a poor 
thing indeed if we could not be so unselfish as to recognize his 
needs as more urgent than our own. Is it too much to hope that, 
even before we leave this hospitable city, we may have some 
assurance that full justice shall be done in this matter ? 



3 

It is a familiar fact that there are epochs in the history of a 
science when it requires new vigour ; when new branches are put 
forth and old branches bud afresh or blossom more plenteously. 
The vivifying cause is generally to be found either in the majestic 
form of the discovery of a new law of Nature, or in the humbler 
guise of the invention of a new instrument of research. The 
history of Astronomy has been rich in such epochs, notable among 
them being that when Newton announced to the world the great 
Law of Gravitation, and that when Galileo first turned his telescope 
to the skies. 

We have within the last half-century been fortunate enough to 
include another great epoch in astronomical history, characterized 
by the birth, almost a twin-birth, of two new scientific weapons — 
the spectroscope and the sensitive film. It is, of course, somewhat 
difficult and scarcely necessary to assign an exact date for the 
origin of either of these ; the spectroscope was perhaps first 
systematically used on the heavenly bodies by Huggins, Rutherfurd, 
and Secchi in the 50's, but we may trace it back to the early work 
of Fraunhofer, who described the spectrum of Sirius ill 181 7, or 
further back to the experiments of Newton with a prism ; and the 
c/yy-plate, which in particular has conferred such benefits on our 
science, had of course its precursors in the collodion plate or the 
daguerreotype. But the greater part of the influence on astronomy 
of both the spectroscope and the photographic method dates from 
the time when the dry plate was first used successfully, not much 
more than a quarter of a century ago ; and in that quarter of a 
century there have been compressed new advances in our know- 
ledge which perhaps will compare favourably with the work of any 
similar period in centuries either past or to come. It is difficult 
to estimate at their true value historical events in which we play a 
part, and any review of such a period undertaken now must 
be necessarily imperfect, for we are advancing so rapidly that our 
point of view is continually changing. But it is an encouraging 
thought that obvious difficulties may enhance interest in the 
attempt nd suggest kindly excuses for its shortcomings. 

From the embarrassingly large number of possible topics which 
the period provides, I have selected that of astronomical photo- 
graphy, and I invite your attention to some characteristic features 
of the photographic method in astronomy, and some reflections 
thereupon. It is scarcely possible to avoid repeating much that 
has been said already, but I hope it will be clear that no claim to 
originality is advanced ; in what follows I wish to claim nothing 
as mine save its imperfections. 

The advantages of the photographic method, which attracted 
attention from the first, may be grouped under three heads— its 
pnver, its facility, and its accuracy. The lines of demarcation are 
ill-defined, but the classification will help us a little, and I proceed 
to consider the groups in this order. 

a2 



The immense power of the photographic method as compared 
with the eye arises from the two facts that (a) by the accumulation 
of long exposures fainter and fainter objects can be detected, and 
that (b) large regions of the heavens can be recorded at the same 
exposure. No property of the photographic plate has excited 
more marvel than the former — that it can detect objects too faint 
to be seen even by our largest telescopes ; objects of whose very 
existence we were in ignorance and should have remained in 
ignorance. Early successes have been followed up by others more 
striking as years have rolled on, as better instruments have been de- 
vised, and the patience of the watchers has proved equal to greater 
strain. It is here that the change from the " wet" plate to the u dry " 
has proved most advantageous. The possibilities with the former 
were limited to the period during which it would remain wet ; 
with the latter, exposures may be continued for hours, days, even 
years — not, of course, continually in the case of astronomical 
photography, for the camera must be closed w r hen daylight 
approaches ; but it can be opened again at nightfall and the ex- 
posure resumed without fault. In this way objects of extraordinary 
faintness have been revealed to us. When Nova Persei had flashed 
into brilliance in 1901, and then slowly faded, long exposure 
photographs of its region revealed to us a taint nebulous structure 
which we could never have seen ; they told us that this structure 
was changing in appearance in a manner which it taxed our 
ingenuity to explain, and about which speculation is still rife. 
But a greater triumph was to come ; even the spectrum of this 
faint object has been photographed. When we consider that in 
the spectrum each point of light in the object is enormously 
diluted by being spread out into a line, the difficulty of this 
undertaking seemed almost prohibitive; but it was not sufficient 
to prevent Mr. Perrine, of the Lick Observatory, from making the 
attempt, and he was deservedly rewarded by success. I may be 
wrong in regarding this success as the high-water mark in this 
direction at the present time, and it will probably be surpassed by 
some new achievement very shortly ; but it will serve to illustrate 
the power of photography in dealing with faint objects. 

But may we here pause for one moment to marvel at the sensi- 
tiveness of the human eye, which is such that it is, after all, not 
left very far behind in the race ? The eye, sensitive as it is merely 
to transient impressions, is no match ultimately for the plate, which 
can act by accumulation. But with similar instruments the plate 
must be exposed for minutes or even hours to seize the impression 
of a faint object which the eye can detect at a glance. There seems 
to be no reason in the nature of things why the eye should not 
have been surpassed in a few T seconds ; and in the future the sen- 
sitiveness of plates may be increased so that this will actually be 
the case, even as in the past there was a time when the sensitive- 
ness was so small that the longest exposure could not compete 
with the eye. But this time is not yet come, and at the present 



moment the eye is still in some departments superior to its rival, 
owing to this very fact, that though it can only see by glances, it 
can use these glances to good effect. In the study of the planets 
the Tnore clumsy method of the photographic plate (which, by 
requiring time for the formation of the image, confuses good 
moments with bad) renders it almost useless as compared with the 
eye ; and again, we have not as yet used photography for daylight 
observations of stars. 

But there is another direction in which the photographic plate 
is immensely superior to the eye in power ; it can record so much 
more at once*. In the able hauds of Prof. Barnard, Dr. Max 
Wolf, and others, this property of the plate has been used to 
record the presence in the sky of vast regions of nebulosity such 
as, we may safely say, the eye would never have satisfactorily 
portrayed, not altogether because of their faintness (for in one of 
his papers Prof. Barnard tells us that he was actually led to 
photograph such a region because he had become vaguely conscious 
of it by eye-observation), but because of their diffusion. It is 
noteworthy that these beautiful photographs were taken with 
comparatively humble instruments, and we may be as yet only on 
the threshold of revelations still to be made in this direction. 

Secondly, the photographic method represents a great advauce 
in facility of manipulation. A familiar example may be taken 
from the domain of planetary discovery. In old time, to recognize 
a new object among numerous fixed stars, it was necessary either 
laboriously to map out the whole region, or to learn it by heart, so 
that it was practically mapped in the brain. Now all this labour 
is avoided ; two photographs of the same region, taken without any 
strain on the memory or the measuring ability of the observer, can 
at a glance, by a simple comparison, give the information that a 
strange object is or is not present — information formerly obtained 
at so much cost. Sometimes, indeed, the cost was so great that the 
information was not obtained at all. For 15 years Hencke searched 
without success for a planet, and for nearly 40 years after the 
discovery of the first four small planets in 1807 no further dis- 
coveries were made, though hundreds were constantly crossing the 
sky, and a dozen new planets are now found every year with 
little trouble. 

* This property has been beautifully illustrated by a lecture-experiment of 
Prof. Barnard. He throws on the screen a picture of a large nebula which the 
photographic plate has no difficulty in portraying all at once ; but the picture 
is in the first instance covered up by a screen, except for a small aperture only, 
and this aperture, he tells his audience, represents all that can be seen by the 
eye at one time, using the giant telescope of the Yerkes Observatory. By 
moving the screen about, different portions of the picture may be viewed suc- 
cessively, as also by moving the telescope about in looking at the sky itself. But 
what a revelation follows when the screen is removed and the full glory of the 
nebula is exhibited at a single glance! We can well understand that the true 
character of these objects was hopelessly misinterpreted by the eye using the 
imperfect method of piecemeal observation which alone was formerly possible. 



6 

Bat though this instance of increase in facility is striking, it is 
far from being the only one or even the most important. Wherever 
we require a record of any kind, whether it be of the configuration 
of stars, or of solar spots, or of the surface of the Moon, or of a 
spectrum, the labour of obtaining it has been enormously reduced 
by the photographic method. Think for a moment of what this 
means in the last instance only — think of the labour involved in 
mapping one single spectrum by eye-observation; of the difficulty 
of settling by such a method any doubtful question of the identity 
of certain lines in the spectrum of a star. A few years ago 
Dr. McClean announced that he had found oxygen in the star 
(3 Crucis. Up to that time this element, so familiar to us on this 
Earth, had appeared to belong to us alone in the Universe, for in 
no spectrum had its lines been detecied. The proof of its existence 
in j3 Crucis depended on the identity of a number of lines in the 
spectrum with some of those of oxygen ; and the measures were 
sufficiently difficult on a photograph, so that for more than a year 
the scientific world refused to pronounce a verdict, iiow long 
would the case have dragged on if only visual measures had been 
possible? "We may fairly doubt whether a definite conclusion 
would ever have been reached at all. By the sheer facility of the 
new method of work we have advanced by leaps and bounds where 
we could only crawl before. 

Thirdly, there has been a great gain in accuracy from the intro- 
duction of photography ; and it is this quality which is above all 
of value in the science of Astronomy *. The wonderful exact- 
ness of the photographic record may perhaps best be characterized 
by saying that it has revealed the deficiencies of all our other 
astronomical apparatus — object-glasses and prisms, clocks, even 
the observer himself. 

It has almost been forgotten that in the early days the accuracy 
of a photograph was doubted. Even now it can scarcely be said 
that we know definitely the stage of refinement at which we must 
begin to expect irregular displacements of the images from dis- 
tortion of the photographic film ; but we have learnt that they do 
not occur in a gross degree, and that other apparatus must be 
improved before we need turn our attention seriously to errors 
arising from such a cause. Consider, for instance, what photography 
has told us about our optical apparatus, which we regard as 
having reached a high stage of perfection. We are accustomed 
to think of properly made optical apparatus as being sufficiently 
similar in all its parts ; it is tacitly assumed in the principle of 

* Two things may be measured on a photographic plate — the position of an 
object, or the density of the image; the former being an indication of its 
position in the heavens, and the latter of its brightness. With the latter topic 
I do not propose to deal, for the reason that it is in the hands of a much abler 
and more experienced exponent; but the former alone will provide enough 
food for reflection. 



the heliometer, for example, that one half of the object-glass is 
sufficiently similar to the other. JBut a stock adjustment recently 
adopted in photographing a spectrum for accurate measurement 
exhibits clearly the errors of this assumption. Photographs are 
taken of the spectrum through the two halves of the objective; 
and if they were properly similar the lines in the two halves of 
the spectrum should fit exactly. A mere glance is usually 
sufficient to show discordances. It is true that one of the 
photographs is taken through the thick half of the prism and the 
other through the thin, so that errors of the prism are included ; 
but these, again, are optical errors. They are, however, not the 
only sources of error which at present mask photographic imper- 
fections. Glass plares are not flat, and this want of flatness 
introduces sensible errors. Even with the great improvements in 
our driving-clocks which were called for immediately photographs 
were to be taken — with electrical control and careful watching on 
the part of the observer, — there is apt to creep in a " driving-error " 
"which gives bright stars a spurious displacement relatively to 
faint. We must get flatter plates, better driving-clocks, and 
watch more carefully before we can certainly accuse our photo- 
graphs of a failure in accuracy. Nevertheless, there are indications 
that we may be near the limit of accuracy even now. Examination 
of the re'seau hues on various plates appears to show small dis- 
placements for which no cause has vet been assigned ; and the 
end of our tether may not be far away. But as yet we have not 
been pulled up short, aud there is hope that the warning may be, 
as on one or two previous occasions, a false alarm. 

Such being the accuracy of the photographic method, it is 
surprising that it should not as yet have been more fully adopted 
in that field of work where accuracy is of the greatest importance — 
namely, in what is called fundamental work, with the transit- 
circle or other meridian instruments. The adoption of new 
methods is always a slow process and there are at least two 
classes of difficulties which hinder it. The first class has its origin 
m the instinctive conservatism of human nature, wherein men of 
science differ little from their fellows. The second has to do 
with available capital : and in this respect we are distinctly at a 
disadvantage compared with other men ; for when a new instru- 
ment of general utility is invented, at once a large amount of 
capital is invested in working out the details and improving them 
to the utmost, whereas for a scientific instrument no such funds 
are available. Think, for instance, of the money spent in perfecting 
the bicycle, and the time occupied in developing it from the 
earliest forms to those with which we are now familiar — from the 
"boneshaker" of the sixties through the high bicycle which we saw 
20 years ago, to the modern j machine. Think, too, how totally 
unexpected have been some of the incidents in the history of this 
machine — such as the introduction of pneumatic tyres, or its use 



8 

by ladies *. In the case of such an Instrument, now universally 
adopted, if rapid development could have been secured by expendi- 
ture of money and brains, surely enough of both commodities 
were forthcoming to attain that end ; and yet simplicity and 
finality have probably not yet been attained in a period of 30 years. 
When we compare the small amount of money and especially the 
small number of persons that can be devoted to the perfection of 
a new scientific method, snch as the use of photography in 
astronomy, it will excite little suprise that progress during the 
same period of 30 years has been slower. In commerce old 
machines can be thrown on the scrap-heap when improvements 
suggest themselves ; but who can afford to throw away an old 
transit-circle? The very fact that it has been in use for many 
years renders its continued use in each succeeding year the more 
important from considerations of continuity. 

It is doubtless for such reasons as these that little has yet been 
done in the way of utilizing photography for meridian observation. 
Although one or two meritorious beginnings have beon made, 
which have sufficed to show that there are no insuperable diffi- 
culties in the way, up to the present moment no meridian 
instrument of repute is in regular work using the photographic 
method. And this fact canuot, after all, be completely explained 
by the reasons above mentioned. Opportunities for setting up 
costly new instruments do not occur frequently in astronomy, 
but they do occur. In the last decade, for instance, large transit- 
circles have been set up both at Greenwich and the Cape of Grood 
Hope ; but in neither instance has any attempt been made to adopt 
the photographic method. The Washington Observatory was 
reconstructed well within the period since the great advantages of 
photography have been recognized ; and yet not even in the 
United States, the land of enterprise, was a start then made in a 
direction in which it is certain that we must some day travel. 
That day has probably been deferred by the stimulation of com- 
peting methods which a new one brings with it. When electric 
light was first introduced into England, the gas companies, 
stimulated by the stress of competition, adopted a new and 
improved form of light (the incandescent gas) which put them at 
a much less serious disadvantage compared with their new rival. 
So when photography began to show what new accuracy w 7 as 
attainable in measurement of star-positions, it would almost seem 
as if the devotees of the older visual methods were compelled to 
improve their apparatus in order not to be left wholly behind in 
the race. The registering Micrometer f was produced by Messrs. 
Eepsold, with the astonishing result that the troubles from personal 

* I have in my possession a copy of a work of reference on cycling, dated 
no earlier than 1887, in which it is carefully stated as a deliberate conclusion 
that ladies will never use the machine to any great extent. 

t We have been accustomed hitherto to determine the position of a star by 
observing the instant when it crossed a fixed wire ; but it has long been known 



9 

equation, which have so long been a difficulty in all fundamental 
work, have practically disappeared. 

This beautiful invention has placed the eye once more in a 
position actually superior to the photographic plate ; for with the 
eye we can observe stars in daylight, and so secure information of 
great importance, whereas no photographic method of doing this 
has, as yet, been devised. And there is also the fact that for 
faint stars a long exposure would be required for what the eye 
can accomplish in a few seconds. 

Thus in one or two astronomical channels the effects of the 
rising tide of photography have scarcely yet been felt ; but into 
all the others it has swept with ever growing force. Looking 
back over the 30 years of advance, we may be well satisfied. 
With more funds, and especially with more men, no doubt more 
could have been done : let us even admit that we might have done 
better with the same funds and the same limited staff. But on the 
whole we have been fortunate. At a critical time, when we might 
have felt the want of larger endowments acutely, the need was 
almost anticipated by a stream of benefaction. If this stream had 
its chief source in the United States, its beneficial effects have 
poured over the whole world ; and induced currents have begun 
to flow elsewhere. We may reflect with thankfullness how much 
harder our advance might have been but for the noble gifts to the 
Harvard, the Lick, and the Terkes Observatories : and earnestly 
hope that the cheerful expectations of a great American astronomer, 
that these are but the foreshadowing of much larger gifts to science, 
may be adequately realized. 

May I now turn to one or two of the problems with which this 
new development of our work has brought us face to face ? They 

that two different observers record systematically different instants — they have 
a personal equation. Recently we have learnt that this personal equation 
avries with the brightness of the star observed, and with other circumstances, 
and to make the proper corrections for it has severely taxed our ingenuity and 
involved much work. Before the invention of photography, we might well 
bear this with patience, since it seemed to be inevitable ; but the photo- 
graphic plate, which is free from human errors, offers a way of escape from all 
troubles— at the expense, no doubt, of some little experimenting, but with every 
prospect of speedy success. Eye observation, which had borne this burden 
so long, must get rid of it if it was to march alongside the untrammelled 
photographic method ; and the suprising thing is that it has actually done so. 
The adopted device is extremely simple: replace the fixed wire which the star 
crosses by a wire which moves with the star and registers its own movements. 
The registering is done automatically ; but the motion of the wire is controlled 
by the observer and there is still room for a new form of personal equation in 
this human control. But none manifests itself, probably for the reason that 
we no longer have two senses concerned, but only one. In recording the instant 
when a star crosses a wire we employ either the eye and the ear. or the eye 
and the sense of touch ; and personal equation arises from the different co- 
ordination of the two senses in different people. But in making the wire follow 
the star, the eye alone is concerned, and there is no longer any room for 
difference in "latent period" or other co-ordination of two senses. 



10 

are numerous and serious, and it is impossible to consider many of 
them, perhaps even the most important of them. One of the 
most pressing is the problem of rendering generally accessible the 
vast accumulations of material for study that have been suddenly 
thrust upon our attention. How are our photographs to be stored, 
preserved, and published ? Even now troubles have gathered, and 
time will only multiply them. It is many years since Prof .Pickering 
drew attention to the difficulties in storing the photographic plates 
taken at the Harvard Observatory ; when many thousands of photo- 
graphs have been accumulated, not only the space they occupy but 
the actual weight of glass is an embirrassment. And there seems 
to be no doubt concerning the duty of accumulation. May I confess 
an early and mistaken view which I formulated on this matter ? I 
reasoned thus : — The proper moment for making use of a photograph 
taken last night is to-day. It is useless to defer the examination 
until to-morrow, for there will then be new photographs claiming 
attention. Hence it is unscientific to take more photographs than 
can be dealt with immediately. This seemed to be a plausible 
argument and to show a way out of the difficulty, for if a photograph 
had once been adequately examined, it need not be stored so care- 
fully, and there would not in any case be many to store. But 
Prof. Pickering has demonstrated many times over that the view 
is untenable. By taking photographs almost recklessly and without 
any hope of dealing with even a fraction of them, he has created 
the possibility of tracing the history of celestial events backivards. 
When new objects are discovered he can go to his shelves and tell 
us how long they were visible previous to discovery ; and this 
information is so valuable that w 7 e must certainly arrange our 
future plans with reference to it. It is quite certain that .we must 
be prepared to deal with enormous accumulations of places, to 
store them in proper order, and to catalogue them ; and if it has 
already been found difficult to do this for the collection of a 
single observatory during twenty years, what can we look for 
in the centuries to come ? 

Possibly the second difficulty, that of preservation, may be an 
antidote to the first. It is by no means certain that our photo- 
graphs will last long ; and if not, there will be a natural limit to 
the time during which they need he kept. Sir William Crookes 
has, however, reminded us that by toning them, by substituting 
sturdy gold for the perishable silver, we may prolong their life 
indefinitely, though this will, of course, sensibly increase the cost 
of each plate. As yet I have not heard of any toning process being 
systematically adopted. Our course is, however, comparatively 
clear in this direction ; it would seem imperative that a selection 
of the earliest photographs at any rate should be carefully toned, 
so that they mav be available for comparison in years as far 
distant as possible. Although this is a matter of detail, it seems 
to me to compare in importance with almost any practical question 
which may claim the attention of astronomers ; and if some 



11 

decision of the kind were the only outcome of this gathering, I 
think we might be well content with the result. 

The question of publication is chiefly one of funds, and is onlv 
worthy of special remark because these particular funds are so 
often forgotten in planning enterprises. I need not labour the 
point, for the experience of any astronomer will supply him with 
plenty of instances. The difficulties of publication have much in 
common with those of storage ; they will increase year by year, 
and even when the money for printing has been found, the storage 
of publications received from other observatories will itself become 
an embarrassment. There is, however, one way in which some 
of the stress may be relieved, namely by efficient cataloguing. If 
we have before us a list of all the photographs existing in the 
world, and know that we can send for a copy of any one of them 
which may be required, it is no longer necessary to have copies of all. 
This applies, of course, to other publications as well ; and though 
we may take some time to grow out of the sentimental desire for 
a complete library, and though the existence of a few such complete 
institutions may always be desirable, I venture to think that many 
observatories will ultimately be driven to the plan of acquiring only 
what is certainly and immediately useful, depending on temporary 
loans from central institutions for other material. 

But there is a class of problems differing totally in character 
from these practical questions of storage and preservation of 
plates. A period of suddenly increased activity such as we have 
been passing through in astronomy is not without important 
effects on astronomers themselves. The human element in our 
scientific work is sometimes overlooked and generally accorded 
only a subordinate importance ; but coming as I do from an old 
university devoted to the Humanities, I may be perhaps forgiven 
for calling attention to a few human considerations. In the first 
place, I have felt some anxiety lately for that very important body 
of astronomers who are sometimes called amateurs, though the 
name is open to criticism — those whose opportuuities for work are 
restricted to a more or less limited leisure. It is a body which is 
somewhat sensitive to the feeling that astronomical work has gone 
beyond them, that in the presence of large instruments and of the 
special knowledge acquired by those using them, their own efforts 
and their own humbler instruments are no longer of any value. 
If I am right in supposing that this feeliug has been called into 
existence lately by the rapid advances made in photography, it is 
certainly not for the first time. At previous epochs this diffidence 
has found expression and has, I am glad to say, been met by careful 
contradiction ; but it is necessary to repeat the expostulation again 
and again, for the anxiety is apt to crop up with every new de- 
velopment of astronomical activity. 

The early days of photography were better ones than usual for 
the amateur ; indeed the introduction of the photographic method 
is largely due to the work of such men as Eutherf urd and Draper 



12 

in America, De la Rue and Common in England. But now that 
we have passed beyond the stage when each new plate taken was 
a revelation ; now that we are tolerably familiar with, at any rate, 
the main types of possible photographs which can be taken with 
modest apparatus ; more especially now that we have begun to 
discuss in elaborate detail the measurement of star-positions or of 
stellar spectra, the old shyness is beginning to crop up again. But 
it is of the utmost importance that this shyness should be zealously 
overcome. Perhaps, after all, it is not sufficient to assert that there 
is still good work for amateurs to do, nor even to mention a few 
instances of such work urgently required ; perhaps it should be 
made easier for them to follow what is being done. Especially do 
we want more and better books, written by the best men in each 
subject. The original memoir, though it may be the proper form 
of publication for the workers themselves, does not satisfy all 
requirements. There is much to be done in the way of extension 
and collation before the work can be presented in a form attractive 
to those who would gladly keep in touch with it if the process 
could be made a little easier. Huxley was constantly urging 
scientific men that it was not sufficient to attain results ; they must 
also express them in an intelligible and attractive form. Of course 
it is not easy for the same man to do both. There are few who 
could have determined, like Schiaparelli, that the period of rotation 
of the planet Mercury was 88 days instead of t ; but there are 
fewer still who, after making the discovery, could have given the 
beautiful lecture which he gave before the King of Italy, developing 
fully in attractive detail the consequences of the discovery ; and 
yet it is probably true that many more could make, at any rate, an 
attempt in this direction, if adequate opportunity and inducement 
were provided. Could not a part of the sums available for the 
endowment of research be devoted to the endowment of text-books? 
It is of course an inducement to write such a book that it is a good 
thing well done ; but in the case of a scientific worker this is 
scarcely sufficient, because the same could be said of his continuing 
his particular work. If we ask him to pause, and render the 
treasures he has collected accessible to others, there must be some 
additional inducement. Publishers are not able to offer pecuniary 
encouragement, because books of the type I have in mind would 
not appeal to a very large public. But why should they not be 
subsidized ? I do not think it need be a very costly business, if the 
money were placed in the hands of a central body to issue invitations 
for books to be written. An invitation would be in itself a com- 
pliment ; and the actual pecuniary value of the inducement would 
shrink in importance, just as the actual amount of gold in a medal 
awarded by one of our leading scientific societies is not very 
seriously regarded. It may be objected that to ask the best men 
to write text-books is to set them to inferior work, and so to delay 
true scientific progress ; but are we sure that the real march of 
science is beiug delayed ? There are pauses in a journey which 



13 

merely waste time ; but there are others without which the whole 
jonrney may be delayed or prevented, as when a man should neglect 
to rest and feed the horse which carries him. 

But the development of photography has brought with it much 
more than a recurrence of diffidence in some amateurs ; it has fore- 
shadowed a serious rearrangement of astronomical work generally 
— a new division of labour and a new system of cooperation. To 
quote one notable instance : a very small number of observatories 
could take enough photographs to keep the whole world busy 
-examining or measuring them, and we are already face to face 
with the question whether this is a desirable arrangement. Let 
me give a concrete example of this modern situation. In the 
winter 1 900-1 the small planet Eros offered a specially favourable 
opportunity for determining the solar parallax, and some thousands 
of photographs were taken at a number of observatories for the 
purpose. It is not yet very clear how a definitive result will be 
obtained from the mass of material accumulated, most of which is 
being dealt with in a very leisurely manner : but a small portion 
of it has been discussed by Mr. A. R. Hinks, of Cambridge, and 
one of the many important results obtained by him in a recently- 
published paper (Mon. Not. R. A. S., June 1904) is this : that the 
plates taken at the Lick Observatory are susceptible of such 
accurate measurement, and so numerous, that a determination of 
the solar parallax from them alone would have a weight nearly 
equal to that from the whole mass of material. If the Lick plates 
can be measured and reduced, it will not much matter if all the 
others are destroyed. Whence we may deduce two conclusions : 
firstly, that it is eminently desirable that these beautiful pictures 
should be measured and reduced as soon as possible ; secondly, 
that we must consider future plans of campaign very carefully if 
we are to avoid waste of work and discouragement of workers. It 
is tolerably easy to reach the first precise conclusion ; I wish it 
were easier to arrive at something more definite in regard to the 
second. It seems clear that we may expect some readjustment of 
the relations between the better-equipped observatories and those 
less fortunate, but it is not at all clear what direction that 
readjustment should take. One possibility is indicated by the 
instance before us : the discussion of the Lick photographs was 
not conducted at the Lick Observatory, but at Cambridge : the 
price paid for the fine climate of Mount Hamilton is the accumu- 
lation of work beyond the powers of the staff to deal with, and 
the new division of labour may be, for the observatories with fine 
climates and equipment to take the photographs, and astronomers 
elsewhere to measure and discuss them. Prof. Kapteyn has set 
us a noble and well-known example in this direction, and in view 
of the pressing need for a study of many photographs already 
taken, it is to be hoped that his example will be followed, es- 
pecially in cases similar to his own, where no observatory is in 
existence. If in such cases the investigator will set up a measuring 



14 

machine instead of a telescope, he will deserve the gratitude of the 
astronomical world. 

But the case is not so clear when a telescope is already in 
existence. Mr. Hinks had a fine telescope at Cambridge, and it 
required some self-denial on his part to give up observing for a 
time in order to discuss the Lick photographs and others. If the 
accumulations already made, and others certain to be made in the 
future, are to be dealt with, this kind of self-denial must certainly 
be exercised, but it does not seem quite clear that it should always 
fall to the lot of those with a modest equipment. Considerations 
of strict economy might suggest this view, but there is a human 
side to the argument which is not unimportant. The danger that 
the minor observatories should feel their work unnecessary is even 
graver than the similar possibility in the case of amateurs already 
mentioned, and calls for prompt attention from astronomers 
generally if it is to be averted. It is the more serious because of 
another set of considerations of a quite different kind, viz., the 
funds available for research show a rather alarming tendency to 
accumulate in the hands of a few large observatories, leaving many 
astronomers who could do useful work without the means of 
doing it. A conspicuous example is afforded by the present state 
of the work for the Astrographic Chart initiated in Paris seventeen 
years ago. On the one hand, a few of the large observatories have 
easily acquired funds not only for taking and measuring the plates 
and printing the results, but for publishing an expensive set of 
charts which will be of very little use to anyone; on the other 
hand, some of their colleagues have found the utmost difficulty in 
getting funds for even taking the plates ; others have got so far 
but cannot proceed to measure them ; and very few indeed have 
yet funds for printing. If there had been a true spirit of 
cooperation for the general good in this enterprise, surely some 
of the funds being squandered on the comparatively useless charts 
would have been devoted to the proper complerion of the only part 
of the scheme which has a chance of fulfilment. I do not mean to 
imply that this would have been an easy matter to arrange, but it 
is noteworthy that no attempt in this direction has been made, and 
that as a consequence a promising scheme is doomed to failure in 
one important particular. For though the survey of the whole sky 
to the nth magnitude may some day be completed, it will be sadly i 
lacking in homogeneity. Some sections are finished before others 
are begun, so that in the vital matter of epoch we shall have a 
scrappy and straggling series instead of a compact whole. 

Cooperation in scientific work, the necessity of which is being 
borne in upon us from all sides, is nevertheless beset with diffi- 
culties, and no doubt we shall only reach success through a series 
of failures, but we shall reach it the more rapidly if we note care- 
fully the weaknesses of successive attempts. In the particular 
scheme of the Astrographic Chart, I think an error which should 



15 

be avoided in future was made by those who have access to the 
chief sources of astronomical endowment. They have made the 
enterprise doubly difficult for their colleagues : firstly, by setting a 
standard of work which was unattainable with limited resources ; 
and secondly by depleting the reserves which might have gone to 
assist the weaker observatories. 

It is easier to draw attention to these modern tendencies than 
to suggest a remedy for them. It may, perhaps, be questioned 
whether a remedy is either possible or necessary ; it may be 
urged that it is both inevitable and desirable that astro- 
nomical observation should gravitate more and more to those 
well-equipped observatories where it can be best conducted, and 
that new resources will obtain the greatest results when added 
to a working capital which is already large. From the purely 
economical point of view of getting results most rapidly, these 
conclusions may be true. But if we look at the human side of 
the question I hope we shall dissent from them ; if we think first 
of astronomers rather than of the accumulation of astronomical 
facts, I hope we shall admit that something must be done to check 
the excessive specialization and the inequalities of opportunity 
towards which there is a danger of our drifting. We cannot 
afford the division of astronomers into two types : one isolated in 
a well-equipped observatory in a fine but rather inaccessible 
climate, spending his whole time in observing or taking photo- 
graphs ; another in the midst of civilization, enjoying all the 
advantages of intercourse with other scientific men, but with no 
telescope worth using, and dependent for his material on the 
observations made by others. Some division of labour in this way 
is doubtless advantageous, but we must beware lest the division 
become too sharply pronounced. Will it be possible to prevent 
its undue growth by some alternation of duties ? Can the hermit 
observer and the university professor take turn and turn about to 
the common benefit ? The proposal is perhaps a little revolutionary, 
and has the obvious disadvantages of inconvenience and expense at 
the epochs of change ; but I do not think it should be set aside on 
these grounds. 

I must admit, however, that I am not ready with a panacea. It 
has been chiefly my object to draw attention to some modern 
tendencies in astronomical work, hoping that the remedies may be 
evolved from a general consideration of them. Such questions of 
the relationship of the worker to his work are even harder to solve 
than those we meet with in the work itself. But there is at least 
this excuse for noticing them on an occasion like the present, that 
they are, to some extent, common to all departments of knowledge, 
and our difficulties may come to the notice of others who have had 
occasion to consider them in other connections and may be able 
to help us. Or, again, we may take the more flattering view that 
the human problems of Astronomy to-day may be those of some 



16 

other science to-morrow ; for Astronomy is one of the oldest of the 
sciences, and has already passed through many stages through 
which others must pass. In any case we must deal with these 
problems in the sight of all men ; and of all the consequences 
entailed by our lately-acquired opportunities, none are more 
interesting and none can be more important to us than those 
affecting the astronomer himself. 



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